Going the extra step

Polystyrene recycling

Going the extra step

A manufacturer of extruders and continuous mixers has developed a method to capture and reuse a greenhouse gas that usually escapes into the atmosphere during polystyrene (PS) recycling.

The process developed by Technical Process & Engineering Inc. (TPEI), Lehighton, Pennsylvania, captures residual pentane gas used as a foaming agent in PS products. The pentane can be reused as a gas or can be liquefied and sold.

“This is a greenhouse gas, so keeping it out of the atmosphere is important,” TPEI President Harold Schafer says. “There is also danger of explosion or fire if too much builds up when it is vented into the atmosphere.”

TPEI started work on the system when a customer that uses recycled PS said it wanted to make greener products. The company, which is recycling PS beads that contain 6 percent pentane into a plastic-lumber-type product, required the material to retain its quality and characteristics.

TPEI’s single-screw extruder with a continuous mixer mounted on top normally vents gases released during recycling into the atmosphere. To capture these gases, TPEI added a third-party scrubber and cooling system to the vent port. The recovered pentane liquefies below 90 degrees Fahrenheit.

The customer for whom TPEI developed the first system plans to use it to boost the propane heating system in its plant. The company declined to be identified.

“There is not enough pentane captured to run an entire heating system, but it gives them a nice boost,” Schafer says.

The scrubber and cooling system add about 20 percent to the cost of its standard mixer and extruder and are now commercially available from TPEI.

The pentane-recovery system is scalable and works on extruders with 500 to 12,000 pounds per hour of output.

“I think there is a market for this equipment,” Schafer says. “When we ran the trials, the PS coming out was not degraded. The finished product had very good properties.”

He adds, “But preventing a greenhouse gas from escaping into the atmosphere was the driving force for our first customer. He wanted a green product, and this system will deliver.”